Positive photoresist having improved processing properties

ABSTRACT

Polymers having a molecular weight (weight average) M w  from 10 3  to 10 6 , comprising recurring structural units of the formulae (I), (IIa) and (IIb) ##STR1## in which R 1  is hydrogen or methyl, Y is a direct bond or a divalent radical of the formula (III) ##STR2## in which Z is a C 1  -C 6  alkylene group bound to the phenyl nucleus, 
     OR 2  is an acid-cleavable radical, 
     in which R 2  is C 4  -C 10  tert-alkyl, allyl, cyclohex-2-enyl, C 6  -C 14  aryl or C 7  -C 16  aralkyl which are unsubstituted or mono- or poly-substituted by C 1  -C 6  alkyl groups, C 1  -C 6  alkoxy groups or halogen atoms, trialkylsilyl or a group of the formulae (IV)-(VII) ##STR3## in which R 8  is C 1  -C 6  alkyl, or C 6  -C 14  aryl or C 7  -C 16  aralkyl which are unsubstituted or mono- or poly-substituted by C 1  -C 6  alkyl groups, C 1  -C 6  alkoxy groups or halogen atoms, 
     R 3  and R 4  independently of one another are hydrogen, C 1  -C 6  alkyl groups, C 1  -C 6  alkoxy groups or halogen atoms, 
     R 5  and R 6  independently of one another are hydrogen or methyl, 
     X is C 1  -C 6  alkylene and R 7  is C 1  -C 6  alkyl, or C 6  -C 14  aryl or C 7  -C 16  aralkyl which are unsubstituted or mono- or poly-substituted by C 1  -C 6  alkyl groups, C 1  -C 6  alkoxy groups or halogen atoms, or is --CO--R 8  in which R 8  is as defined in formula (IV), 
     are suitable for use in DUV positive photoresists which show greatly reduced delay time effects and are distinguished by a high thermal stability and high resolution capacity.

This application is a division of application Ser. No. 08/160,818, filedDec. 3, 1993.

The present invention relates to polymers based on derivatives ofstyrene and maleimide, to radiation-sensitive compositions containingthese polymers, to the use of such compositions as positive photoresistand to the protective layers and relief structures produced from thesecompositions.

Lithography in the deep UV region (DUV, wavelengths of about 200-300 nm)is particularly suitable for producing relief structures in thesubmicron range.

In EP-A 410 794, negative DUV photoresists are described which comprisespecific acid-hardenable copolymers and terpolymers based on styrene andhydroxymaleimides. These negative resists can be developed underaqueous-alkaline conditions.

In general, however, positive photoresists are more suitable forproducing images of certain geometrical structures, for example isolatedlines, equidistant lines or interspacious or contact holes, and they areusually preferred for such applications over comparable negativeresists.

Positive photoresist compositions based onpoly[p-tert-butoxycarbonyloxystyrene] and onium salts, suitable forlithography in the UV region, are known, for example, from U.S. Pat. 4491 628.

Similar resist formulations comprisingpoly[p-2-tetrahydropyranyloxy]styrene are described in EP-A 342 498.

However, these chemically intensified positive photoresists show, as afunction of the so-called delay time, structural changes which manifestthemselves in more or less pronounced T-shaped profiles (T-topping) ofthe developed structures. Delay time signifies the time differencebetween exposure and the subsequent post-exposure bake which is as arule necessary in order to ensure complete reaction of theacid-sensitive groups with the acid generated by the exposure.

Traces of organic bases in the surrounding atmosphere are probablyresponsible for these delay time effects. In "Deep-UV Resists withimproved delay capacities", SPIE Volume 1672 (Adv. Resist Technol.Process.), 46-55 (1992), D. J. H. Funhoff, H. Binder and R. Schwalmdiscuss various measures for suppressing this undesired effect, forexample the application of an additional protective coating, anexpensive filtration of the air, or the use of special developers forremoving the T-tops, and finally recommend the use of specificadditives. The stability, achieved in this way, towards delay timeeffects involves, however, a certain loss of sensitivity.

It has now been found that, when specific polymers based on derivativesof styrene and maleimide are used as photoresist materials, the delaytime effects described above are largely suppressed without addition ofadditives or the insertion of additional process steps.

The present invention relates to polymers having a molecular weight(weight average) M_(w) from 10³ to 10⁶, comprising recurring structuralunits of the formulae (I), (IIa) and (IIb) ##STR4## in which R₁ ishydrogen or methyl, Y is a direct bond or a divalent radical of theformula (III) ##STR5## in which Z is a C₁ -C₆ alkylene group bound tothe phenyl nucleus,

OR₂ is an acid-cleavable radical,

in which R₂ is C₄ -C₁₀ tert-alkyl, allyl, cyclohex-2-enyl, C₆ -C₁₄ arylor C₇ -C₁₆ aralkyl which are unsubstituted or mono- or poly-substitutedby C₁ -C₆ alkyl groups, C₁ -C₆ alkoxy groups or halogen atoms,trialkylsilyl or a group of the formulae (IV)-(VII) ##STR6## in which R₈is C₁ -C₆ alkyl, or C₆ -C₁₄ aryl or C₇ -C₆ aralkyl which areunsubstituted or mono- or poly-substituted by C₁ -C₆ alkyl groups, C₁-C₆ alkoxy groups or halogen atoms,

R₃ and R₄ independently of one another are hydrogen, C₁ -C₆ alkylgroups, C₁ -C₆ alkoxy groups or halogen atoms,

R₅ and R₆ independently of one another are hydrogen or methyl,

X is C₁ -C₆ alkylene and R₇ is C₁ -C₆ alkyl, or C₆ -C₁₄ aryl or C₇ -C₁₆aralkyl which are unsubstituted or mono- or poly-substituted by C₁ -C₆alkyl groups, C₁ -C₆ alkoxy groups or halogen atoms, or is --CO--R₈ inwhich R₈ is as defined in formula (IV).

R₁ is preferably hydrogen.

Y is preferably a direct bond.

Alkyl or alkoxy groups R₂, R₃, R₄, R₇ or R₈, or alkyl or alkoxy groupsas substituents of allyl, cyclohex-2-enyl, aryl or aralkyl groups can bestraight-chain or branched. Examples are: methyl, ethyl, n-propyl,i-propyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, neopentyl, n-hexyl,methoxy, ethoxy, n-propoxy, i-propoxy, n-butoxy, sec-butoxy,tert-butoxy, n-pentoxy, neopentoxy and n-hexoxy.

Halogen atoms as radicals R₃ or R₄, or as substituents of allyl,cyclohex-2-enyl, aryl or aralkyl groups, are preferably bromine orchlorine atoms.

Unsubstituted or substituted aryl or aralkyl groups R₂, R₇ or R₈ are,for example, phenyl, tolyl, xylyl, mesityl, isityl, naphthyl, anthryl,phenanthryl, fluorenyl, biphenyl, benzyl, 2-phenylethyl,2-phenylprop-2-yl or tolylmethyl.

Unsubstituted or substituted allyl groups R₂ are preferably allyl,methallyl or especially 3-methylbut-2-enyl.

C₁ -C₆ Alkylene groups Y or X can likewise be straight-chain orbranched. Examples are methylene, ethylene, propylene, 2,2-propanediyl,trimethylene, tetramethylene and hexamethylene.

Preferred polymers according to the invention comprise recurringstructural units of the formula (I) in which R₁, R₃ and R₄ are hydrogen,Y is a direct bond and R₂ is C₄ -C₁₀ tert-alkyl, trimethylsilyl, allylwhich is unsubstituted or mono- or poly-substituted by C₁ -C₆ alkylgroups, cyclohex-2-enyl or a group of the formulae (IV)-(VII) in whichR₈ is C₁ -C₄ alkyl or phenyl.

Particularly preferred are polymers comprising recurring structuralunits of the formula (I) in which R₁, R₃ and R₄ are hydrogen, Y is adirect bond and R₂ is tert-butyl, tert-butoxycarbonyl,3-methylbut-2-enyl or a group of the formula (V).

In the structural units of the formula (IIa), R₅ and R₆ are preferablyhydrogen and X is preferably methylene.

Also preferred are polymers comprising recurring structural units of theformula (IIb) in which R₅ and R₆ are hydrogen, R₇ is C₁ -C₄ alkyl,phenyl or --CO--R₈, in which R₈ is C₁ -C₄ alkyl or phenyl, and X ismethylene, ethylene, trimethylene or tetramethylene.

Particularly preferred are polymers comprising recurring structuralunits of the formula (IIb) in which R₅ and R₆ are hydrogen, R₇ is methylor acetyl and X is methylene or ethylene.

The polymers according to the invention preferably comprise 10-75 mol %,in particular 20-50 mol %, of structural units of the formula (IIa) and25-90 mol %, in particular 50-80 mol %, of structural units of theformula (IIb), relative to 100 mol % structural units of the formula(I).

The molecular weight (weight average) of these polymers is preferably5000-500 000, in particular 20 000-250 000.

The polymers according to the invention can be prepared in a knownmanner by free-radical polymerization of compounds of the formulae (IX),(Xa) and (Xb) ##STR7## in which R₁ to R₈, Y and X are as defined above.

The free-radical copolymerization can be carded out with application ofvarious techniques. These have been described, for example, by S.Sandler and W. Karo in "Polymer Synthesis", Volume 1, pages 3-17, 1968,Academic Press, New York. Examples of usual polymerization processes arethe polymerization in bulk or in solvents, and also emulsionpolymerization, suspension polymerization or precipitationpolymerization. If desired, the molecular weight can be adjusted by theaddition of small quantities of a regulator (for exampledodecylmercaptan).

The starting products of the formulae (IX), (Xa) and (Xb) are known orcan be prepared by known methods.

The compounds of the formula (IX), in which Y is a direct bond and R₂ isC₁ -C₆ alkyl, C₁ -C₆ alkoxy, C₆ -C₁₄ aryl, C₇ -C₁₅ aralkyl,trimethylsilyl or C₂ -C₈ alkenyl, can be obtained, for example, bycondensation of unsubstituted or substituted p-hydroxystyrene orα-methyl-p-hydroxystyrene with the corresponding alkyl, alkoxy, aryl,aralkyl, trimethylsilyl or alkenyl halides or tosylates in the presenceof bases.

Analogously, compounds of the formula (IX), in which Y is a direct bondand R₂ is a group of the formula (IV), are accessible from unsubstitutedor substituted p-hydroxystyrene or α-methyl-p-hydroxystyrene and thecorresponding chlorocarbonates.

The compounds of the formula (IX), in which Y is a direct bond and R₂ isa group of the formulae (V)-(VII), can be synthesized, for example, fromunsubstituted or substituted p-hydroxystyrene orα-methyl-p-hydroxystyrene by reaction with 2,3-dihydropyran, 5-alkoxy-,5-aryloxy- or 5-aralkoxy-2,3-dihydropyran or 2,3-dihydrofuran in acidsolution.

The compounds of the formula (IX), in which Y is a divalent radical ofthe formula (III), can be prepared analogously from the correspondingacrylates or methacrylates.

Examples of suitable compounds of the formula (IX) are 4-methoxystyrene,α-methyl-4-methoxystyrene, 4-ethoxystyrene, 4-tert-butoxystyrene,4-phenoxystyrene, 4-benzyloxystyrene, 4-trimethylsilyloxystyrene,4-allyloxystyrene, 4-methallyloxystyrene,4-(tert-butylcarbonyloxy)styrene, 4-(2-tetrahydropyranyloxy)styrene,4-(2-tetrahydrofuranyloxy)styrene, 4-(3-methylbut-2-enyloxy)styrene,4-(2-tetrahydropyranyloxy)benzyl methacrylate and4-(2-tetrahydropyranyloxy)benzyl acrylate.

The compounds of the formulae (Xa) and (Xb) are likewise known or can beprepared by known processes from maleimide or methyl- ordimethyl-maleimide, for example by reacting maleimide in the presence ofbases with a halide or a tosylate of the formula LG--X--OH orLG--X--OR₇, in which X and R₇ are as defined above and LG is halogen orCH₃ --C₆ H₄ --SO₃.

The synthesis of N-hydroxymethylmaleimide from maleimide andformaldehyde in the presence of NaOH is described, for example, in EP-A410 794.

Examples of suitable compounds of the formulae (Xa) and (Xb) areN-hydroxymethylmaleimide, N-2-hydroxyethylmaleimide,N-3-hydroxypropylmaleimide, N-4-hydroxybutylmaleimide,N-(2-hydroxyprop-2-yl)maleimide, N-methoxymethylmaleimide,N-phenoxymethylmaleimide, N-benzyloxymethylmaleimide,N-2-methoxyethylmaleimide, N-3-methoxypropylmaleimide,N-4-methoxybutylmaleimide, N-acetoxymethylmaleimide andN-(2-acetoxyethyl)maleimide.

The polymerization is in general initiated by a conventional freeradical starter. These include thermal initiators such as azo compounds,for example α,α'-azoisobutyronitrile (AIBN), or peroxides, for examplebenzoyl peroxide, or redox initiator systems such as a mixture ofiron(HI) acetylacetonate, benzoin and benzoyl peroxide, or photochemicalfree-radical formers such as benzoin or benzil dimethylketal.

The polymerization is preferably carded out in solution. The reactiontemperature is in general in the range from 10° to 200° C., preferablybetween 40° and 150° C., particularly preferably between 40° and 100° C.

Solvents which may be present must be inert under the reactionconditions. Possible solvents are, inter alia, aromatic hydrocarbons,chlorinated hydrocarbons, ketones and ethers. Examples are: benzene,toluene, xylenes, ethylbenzene, isopropylbenzene, ethylene chloride,propylene chloride, methylene chloride, chloroform, methyl ethylketones, acetone, cyclohexanone, diethyl ether or tetrahydrofuran.

As mentioned at the outset, the polymers according to the invention arevery suitable as base resins for DUV positive photoresists, which showgreatly reduced delay time effects and have a high resolution capacityand high thermal stability.

The invention thus also relates to radiation-sensitive compositionscomprising

a) at least one polymer according to the invention as defined above and

b) at least one compound which forms an acid under the action of actinicradiation.

Preferably, the compositions according to the invention comprise asfurther component c) a solvent or a solvent mixture.

Moreover, the compositions according to the invention can comprisesolution inhibitors, which reduce the solubility of the composition inconventional alkaline developers, but which are cleaved under the actionof acid in such a way that the remaining reaction products are solublein the developer. Such solution inhibitors are known to those skilled inthe art and are described, for example, in EP-A 329 610 and EP-A 475903.

The compounds b), which form an acid under the action of actinicradiation, can especially be onium salts, such as diazonium salts,sulfonium salts, sulfoxonium salts and iodonium salts, and alsodisulfones. Preferred are sulfonium salts of the formula VIII

    (Ar.sub.1).sub.q (Z.sub.1)(Z.sub.2).sub.s S.sup.⊕ X.sup.⊖(VIII),

in which

Ar₁ is phenyl, naphthyl or phenyl-COCH₂ --, which are unsubstituted orsubstituted by halogen, C₁ -C₄ alkyl, C₁ -C₄ alkoxy, --OH and/or nitro,

Z₁ is C₁ -C₆ alkyl or C₃ -C₇ cycloalkyl and

Z₂ is tetrahydrothienyl, tetrahydrofuryl or hexahydropyryl,

q is 0, 1, 2 or 3,

r is 0, 1 or 2 and

s is 0 or 1, the sum q+r+s being 3, and

X₁ .sup.⊖ is a chloride, bromide or iodide anion, BF₄.sup.⊖, PF₆.sup.⊖,AsF₆.sup.⊖, SbF₆.sup.⊖, FSO.sup.⊖ or the anion of an organic sulfonicacid or carboxylic acid.

Phenyl, naphthyl and phenacyl groups Ar₁ are preferably monosubstituted,in particular by Cl, Br, methyl, methoxy, --OH or nitro. Particularlypreferably, these radicals are unsubstituted. Z₁ is preferably C₁ -C₄alkyl, especially methyl or ethyl. Preferably, q is 2 or 3, r is 1 orzero and s is zero, and especially q is 3, and r and s are zero. Veryparticularly preferably, Ar₁ is unsubstituted phenyl and q is 3.

The anion X₁.sup.⊖ of an organic sulfonic acid or carboxylic acid can bethe anion or aliphatic, cycloaliphatic, carbocyclic-aromatic,heterocyclic-aromatic or araliphatic sulfonic or carboxylic acids. Theseanions can be substituted or unsubstituted. Sulfonic and carboxylicacids of low nucleophily are preferred, for example partiallyfluorinated or perfluorinated derivatives or derivatives which aresubstituted in the position vicinal to the particular acid group.Examples of substituents are halogen such as chlorine or especiallyfluorine, alkyl such as methyl, ethyl or n-propyl, or alkoxy such asmethoxy, ethoxy or n-propoxy.

Examples of aliphatic sulfonic acids are methane-, ethane-, n-propane-,n-butane- and n-hexane-sulfonic acid or the corresponding partiallyfluorinated or perfluorinated derivatives.

Examples of aliphatic carboxylic acids are formic acid, acetic acid,propionic acid, butyric acid, pivalic acid, caproic acid,2-ethylhexylcarboxylic acid and fatty acids such as lauric acid,myristic acid or stearic acid, and also the partially fluorinated orperfluorinated derivatives of these acids.

Examples of cycloaliphatic sulfonic or carboxylic acids arecyclohexanesulfonic acid, cyclohexanecarboxylic acid,camphor-10-sulfonic acid or partially fluorinated or perfluorinatedderivatives thereof.

Examples of carbocyclic-aromatic sulfonic acids are benzenesulfonicacid, toluenesulfonic acid, ethylbenzenesulfonic acid,isopropylbenzenesulfonic acid, dodecylbenzenesulfonic acid ordimethylbenzenesulfonic acid, 2,4,6-triisopropylbenzenesulfonic acid,2,4,6-trimethylbenzenesulfonic acid, naphthalene-mono-, -di- or-tri-sulfonic acids and the corresponding alkylated or partiallyfluorinated or perfluorinated derivatives of these sulfonic acids.

Examples of heterocyclic-aromatic sulfonic acids are pyridine-,thiophene- or pyrrole-sulfonic acids and the corresponding partiallyfluorinated or perfluorinated derivatives of these acids.

Examples of araliphatic sulfonic acids are benzylsulfonic acid,α-methylbenzylsulfonic acid and the corresponding partially fluorinatedor perfluorinated derivatives of these compounds.

Examples of carbocyclic aromatic carboxylic acids are benzoic acid,toluenecarboxylic acid, ethylbenzenecarboxylic acid,isopropylbenzenecarboxylic acid or dimethylbenzenecarboxylic acid,naphthalenecarboxylic acid or anthracenecarboxylic acid and thecorresponding partially fluorinated or perfluorinated derivatives ofthese compounds.

Examples of heterocyclic-aromatic carboxylic acids are pyridine-,thiophene- or pyrrolecarboxylic acid and the corresponding partiallyfluorinated or perfluorinated derivatives of these compounds.

Examples of araliphatic carboxylic acids are benzylcarboxylic acid,α-methylbenzylcarboxylic acid and cinnamic acid as well as thecorresponding partially fluorinated or perfluorinated derivatives ofthese compounds.

Preferably, X₁.sup.⊖ is the monovalent anion of an organic sulfonicacid, in particular of a partially fluorinated or perfluorosulfonicacid. These anions are distinguished by a particularly low nucleophily.

Specific examples of suitable sulfonium salts of the formula VIII aretriphenylsulfonium bromide, triphenylsulfonium chloride,triphenylsulfonium iodide, triphenylsulfonium hexafluorophosphate,triphenylsulfonium hexafluoroantimonate, triphenylsulfoniumhexafluoroarsenate, triphenylsulfonium trifluoromethanesulfonate,diphenylethylsulfonium chloride, phenacyldimethylsulfonium chloride,phenacyltetrahydrothiophenium chloride,4-nitrophenacyltetrahydrothiophenium chloride and4-hydroxy-2-methylphenylhexahydrothiopyrylium chloride.Triphenylsulfonium trifluoromethanesulfonate is particularly preferred.

The compounds b) used can also be iodonium salts of the formula (XI)

    [Ar.sub.2 I.sup.⊕ --Ar.sub.3 ]X.sub.2.sup.⊖    (XI)

in which

Ar₂ and Ar₃ independently of one another are phenyl or naphthyl whichare unsubstituted or substituted by C₁ -C₄ alkyl, C₁ -C₄ alkoxy, halogenand/or nitro, or Ar₂ and Ar₃ together are a group of the formula (XII)##STR8## in which Z₃ is C₁ -C₄ alkyl, C₁ -C₄ alkoxy, halogen or nitroand

Q is a direct bond, --O--, --CH₂ -- or --CO-- and

X₂.sup.⊖ is as defined for X₁.sup.⊖ in the formula (VIII). [Iodoniumsalts of the formula (XI) are described, for example, in GB-A 1 539 192.

Suitable compounds b) are also substances of the formulae (XIII) to(XXII), which generate sulfonic acid under the action of actinicradiation, ##STR9## in which t is 1 or 2, preferably 1,

Z₄ is phenyl or naphthyl which are mono- to tri-substituted by --Cl,--Br, --CN, --NO₂, C₁ -C₄ alkyl, C₁ -C₄ alkoxy, C₁ -C₄ alkylthio,phenoxy, phenylthio, C₁ -C₄ alkylamino, C₂ -C₄ dialkylamino or benzoyl,in particular phenyl which is unsubstituted or monosubstituted by --Cl,methyl or methoxy,

Z₅ is hydrogen or C₁ -C₄ alkyl and

Z₆ is hydrogen, C₁ -C₄ alkyl or phenyl or

Z₅ and Z₆ form, together with the linking C atom, a cyclopentane ring orcyclohexane ring,

Z₇, with t=1, is C₁ -C₁₈ alkyl, phenyl or napthhyl, which areunsubstituted or substituted by C₁ -C₄ alkyl, cyclopentyl, cyclohexyl orcamphoryl and with t=2 is C₂ 14 C₈ alkylene or phenylene,

Z₈ is phenyl or naphthyl which are unsubstituted or mono- totri-substituted by --Cl, --Br, C₁ -C₄ alkyl, C₁ -C₄ alkoxy, C₁ -C₄alkylthio, phenyl, phenoxy, phenylthio, C₁ -C₄ alkyl-CONH--,benzoylamino or dimethylamino, in particular phenyl which isunsubstituted or monosubstituted by --Cl, C₁ -C₄ alkoxy, methylthio orphenyl,

Z₉ is --OH or C₁ -C₄ alkyl,

Z₁₀ is C₁ -C₄ alkyl or phenyl,

Z₁₁ is hydrogen, C₁ -C₄ alkyl, furyl or --CCl₃ or

Z₁₀ and Z₁₁, together with the linking C atom, form a cyclopentane ringor cyclohexane ring,

Z₁₂ and Z₁₃ independently of one another are phenyl which isunsubstituted or substituted by halogen, C₁ -C₄ alkyl or C₁ -C₄ alkoxy,

Z₁₄ is hydrogen or C₁ -C₄ alkyl,

Z₁₅ with t=1, is C₁ -C₆ alkyl, phenyl, naphthyl or benzyl and, with t=2,is C₁ -C₆ alkylene, phenylene or xylylene,

Z₁₆ is phenylene or naphthalene, which are unsubstituted or substitutedby halogen, nitro, C₁ -C₄ alkyl, C₁ -C₄ alkoxy or C₁ -C₄ alkylthio or--CH═CH--,

Z₁₇, with t=1, is C₁ -C₁₂ alkyl, which is unsubstituted or substitutedby halogen, nitro, C₁ -C₄ alkyl or C₁ -C₄ alkoxy or phenyl which isunsubstituted or substituted by halogen, nitro, C₁ -C₄ alkyl or C₁ -C₄alkoxy, and, with t=2, is C₂ -C₈ alkylene or phenylene,

Z₁₈ is phenyl or naphthyl which are unsubstituted or substituted byhalogen, nitro, --CN, C₁ -C₄ alkyl, methoxy, ethoxy, dimethylamino orbenzoyl, and the Z₁₉ independently of one another are C₁ -C₄ alkyl,

R₉ is C₁ -C₁₂ alkyl which is unsubstituted or substituted by halogen,nitro, C₁ -C₄ alkyl or C₁ -C₄ alkoxy, or phenyl which is unsubstitutedor substituted by halogen, nitro, C₁ -C₄ alkyl or C₁ -C₄ alkoxy,

R₁₀ is C₁ -C₄ alkyl, C₁ -C₄ alkoxy or phenyl,

R₁₁ and R₁₂ independently of one another are C₁ -C₄ alkyl, C₁ -C₄ alkoxyor phenyl or together are a radical of the formulae (XXIII), (XXIV) or(XXV) ##STR10## and R₁₃ is C₁ -C₄ alkyl, C₁ -C₄ alkoxy, phenyl orbenzoyl. Alkyl, alkoxy, alkylthio, alkylamino, dialkylamino,alkylcarbamoyl and alkylene groups according to the definition can bestraight-chain or branched, but are preferably straight-chain. Halogenis in particular --Cl or --Br.

Compounds of the formulae (XIII) to (XXII) are described, for example,in EP-A 0 166 682 and 0 085 024 and in the literature cited therein.Particularly preferred compounds of the formulae (XIII) to (XXII) arephenacyl p-methylbenzenesulfonate, benzoin p-toluenesulfonate,α-(p-toluenesulfonyloxy)methylbenzoin-3-(p-toluenesulfonyloxy)-2-hydroxy-2-phenyl-1-phenylpropylether,N-(p-dodecylbenzene-sulfonyloxy)-1,8-naphthalimide andN-(phenylsulfonyloxy)-1,8-naphthalimide.

Further suitable compounds b) are o-nitrobenzaldehydes which rearrangeunder actinic radiation into o-nitrosobenzoic acids, such as1-nitrobenzaldehyde and 2,6-dinitrobenzaldehyde; α-halogenoacylphenonessuch as α, α, α-trichloroacetophenone andp-tert-butyl-α,α,α-trichloroacetophenone, and also sulfonic acid estersof o-hydroxyacylphenones such as 2-hydroxybenzophenone methanesulfonateand 2,4-hydroxybenzophenone bis(methanesulfonate).

Finally, suitable compounds b) are also those which comprisearomatically bound chlorine or bromine, such as are described, forexample, in EP-A0 318 649, for example compounds of the formula (XXVI)##STR11## with at least one aromatically bound chlorine or bromine atom,in which, for example,

p is 0 or 1,

Z₂₀ is --COOH, --OZ₂₃ or --SZ₂₃,

Z₂₁ and Z₂₂ independently of one another are hydrogen, --Cl, --Br, alkylwhich is unsubstituted or substituted by aryl, alkoxy, aryloxy, --OH or--F, or aryl which is unsubstituted or substituted by alkoxy, aryloxy,--OH or halogen,

Z₂₃ is hydrogen, alkyl or aryl which are unsubstituted or substitutedanalogously to Z₂₁, or acyl,

A, with p=0, is hydrogen, --Cl, --Br or alkyl which is unsubstituted orsubstituted analogously to Z₂₁, and, with p=1, is --SO₂ --, propylene orperfluoroalkylene and

B is a group ##STR12## alkylcarbonyl, alkoxycarbonyl or substitutedsulfonylimidocarbonyl.

Examples of such compounds are hexafluorotetrabromobisphenol A,1,1,1-tris-(3,5-dibromo-4-hydroxyphenyl)ethane andN-(2,4,6-tribromophenyl)-N'-(p-toluenesulfonyl)urea.

Compounds b) which are used with particular preference are those of theformula (VIII), in which Ar₁ is phenyl, q is the number 3, r and s arezero, and X₁.sup.⊖ is SbF₆.sup.⊖, AsF₆.sup.⊖, PF₆.sup.⊖, CF₃ SO₃.sup.⊖,C₂ F₅ SO₃.sup.⊖, n--C₃ F₇ SO₃.sup.⊖, n--C₄ F₉ SO₃.sup.⊖, n--C₆ F₁₃SO₃.sup.⊖, n--C₈ F₁₇ SO₃.sup.⊖ or C₆ F₅ SO₃.sup.⊖.

Very particularly preferably, the component b) used istriphenylsulfonium trifluoromethanesulfonate.

The compounds b) axe advantageously employed in a quantity of 0.1-20% byweight, preferably 1-10% by weight and especially 1-6% by weight,relative to the weight of component a).

The compositions according to the invention can comprise furtherconventional additives, for example binders, stabilizers, pigments,dyes, fillers, adhesion promoters, flow agents, wetting agents andplasticizers. Preferably, the compositions are dissolved in suitablesolvents [component c)] for application.

The binder is selected according to the field of application and theproperties demanded for this purpose. Examples of suitable binders arenovolaks which are derived from an aldehyde, preferably formaldehyde,acetaldehyde or furfuraldehyde, but in particular from formaldehyde, anda phenol. The phenolic component of these binders is preferably phenolitself, or also halogenated phenol, for example substituted by one totwo chlorine atoms, preferably p-chlorophenol, or it is a phenolsubstituted by one to two C₁ -C₉ alkyl groups, for example o-, m- orp-cresol, a xylenol, p-tert-butylphenol or p-nonylphenol. However, thephenol component of the preferred novolaks can also be p-phenylphenol,resorcinol, bis(4-hydroxyphenyl)methane or2,2-bis(4-hydroxyphenyl)propane.

Examples of further suitable binders are copolymers of maleic anhydridewith styrene, vinyl ethers or 1-alkenes. Homopolymeric or copolymericacrylates and methacrylates, for example copolymers of methylmethacrylate/ethyl acrylate/methacrylic acid, poly(alkyl methacrylates)or poly(alkyl acrylates) having, for example, 1-20 carbon atoms in thealkyl radical, can also be used as binders.

Preferably, the binder used is an alkali-soluble substance, for examplea novolak (if appropriate, modified as described above),poly(4-hydroxystyrene) or poly(4-hydroxy-3,5-dimethylstyrene),copolymers of maleic anhydride with styrene, vinyl ethers or 1-alkenes,and also copolymers of acrylate or methacrylate esters withethylenically unsaturated acids, for example methacrylic acid or acrylicacid.

The radiation-sensitive compositions according to the invention,dissolved in a solvent or solvent mixture, are outstandingly suitable ascoating agents for substrates of any type, for example wood, textiles,paper, ceramics, glass, plastics such as polyester, polyethyleneterephthalate, polyolefins or cellulose acetate, in particular in theform of films, and also metals such as Al, Cu, Ni, Fe, Zn, Mg or Co, andGaAs, Si or SiO₂ to which an image is to be applied by imagewiseexposure.

The selection of the solvent and the concentration depend mainly on thetype of the composition and on the coating process. The solvent shouldbe inert, i.e. it should not enter any chemical reaction with thecomponents and it should be removable again during drying after coating.Examples of suitable solvents are ketones, ethers and esters, such asmethyl ethyl ketone, 2-heptanone, cyclopentanone, cyclohexanone,γ-butyrolactone, ethyl pyruvate, diethylene glycol dimethyl ether,2-methoxyethanol, 2-ethoxyethanol, 2-ethoxyethyl acetate,1-methoxy-2-propyl acetate, 1,2-dimethoxyethane, ethyl acetate and3-methoxymethyl propionate.

The solution is applied by means of known coating processes uniformly toa substrate, for example by spin-coating, dipping, blade coating,curtain coating methods, brushing, spraying, especially by electrostaticspraying, and reverse roller coating. It is also possible to apply thephotosensitive layer to a temporary flexible support and then to coatthe final substrate, for example a copper-laminated circuit board, bylayer transfer via lamination.

The quantity applied (layer thickness) and the nature of the substrate(layer support) depend on the desired field of application. The layerthickness range comprises in general values from about 0.1 μm to morethan 10 μm.

After coating, the solvent is as a rule removed by drying, and theresult is a layer of the composition according to the invention of thesupport.

The radiation-sensitive compositions according to the invention aresuitable as photoresists for electronics (electroplating resist, etchresist, solder resist), for the production of printing plates such asoffset printing plates or screen printing forms, for use in chemicalmilling or use as microresist in the production of integrated circuits.The possible layer supports and the processing conditions of the coatedsubstrates are correspondingly diverse.

The use of the compositions according to the invention as a positivephotoresist is a further subject of the invention.

Films of polyester, cellulose acetate or plastic-coated papers, forexample, are used for photographic information recordings; speciallytreated aluminium is used for offset printing forms, copper laminatesare used for the production of printed circuits, and silicon wafers areused for the production of integrated circuits. The layer thicknessesfor photographic materials and offset printing forms are as a rule about0.5 μm to 10 μm, and 0.4 to about 2 μm for printed circuits.

For producing relief structures, the substrate coated with thecomposition according to the invention is exposed imagewise. The term"imagewise" exposure comprises exposure through a photomask whichcontains a predetermined pattern, for example a transparency, exposureby a laser beam which is moved, for example under computer control,across the surface of the coated substrate and generates an image inthis way, irradiation with computer-controlled electron beams and alsoirradiation with X-rays or UV light through an appropriate mask.

The radiation sources used can in principle be all lamps which emitradiation in the UV range. Both point light sources and two-dimensionalemitters (lamp carpets) are suitable. Examples are: carbon arc lamps,xenon arc lamps, mercury vapour lamps doped, if appropriate, with metalhalides (metal halide lamps), fluorescent lamps, incandescent argonlamps, electronic flash lamps, photographic floodlights, electron beamsand X-rays. The distance between the lamp and the image materialaccording to the invention can vary depending on the intended use andthe type and/or intensity of the lamp, for example between 2 cm and 150cm. Laser light sources, for example argon ion lasers or crypton ionlasers, are especially suitable. With laser light, the resist can alsobe exposed without a mask, the controlled laser beam writing directly onthe resist layer. In this case, the high sensitivity of the materialsaccording to the invention is very advantageous, since it allows highwriting speeds at relatively low intensity. Printed circuits in theelectronics industry, lithographic offset printing plates or reliefprinting plates as well as photographic image recording materials can beproduced by this method. The high sensitivity of the resists is also ofadvantage for exposure by means of DUV steppers, since very shortexposure times are desirable.

After the exposure, the resist is as a rule subjected to a heattreatment, the so-called post-exposure bake, in order to ensure completereaction of the acid-sensitive groups in the polymer structure with theacid generated by the exposure. The duration and temperature of thispost-exposure bake can vary within wide ranges and depend essentially onthe composition of the acid-sensitive polymer and on the nature of theacid generator used as well as on the concentrations of these twocomponents. Usually, the exposed resist is subjected for a period from afew seconds up to several minutes to temperatures of about 50°-150° C.

Surprisingly, the delay time, during which T-tops do not yet appear, issubstantially extended in the case of the resists according to theinvention, as compared with the hitherto known positive photoresistsystems, for example those described in EP-A 366 590 or EP-A 342 498.

After the imagewise exposure and heat treatment of the material, cardedout in the usual manner, the exposed areas of the photoresist areremoved by dissolving them out in a developer.

The selection of the particular developer depends on the nature of thephotoresist, in particular on the nature of the binder used or of thephotolysis products formed. The developer can comprise aqueous solutionsof bases, to which organic solvents or mixtures thereof have been addedif necessary.

Particularly preferred developers are aqueous alkaline solutions, suchas are also used for the development of naphthoquinone-diazide layers.These include in particular aqueous solutions of alkali metal silicates,phosphates, hydroxides and carbonates. If appropriate, minor quantitiesof wetting agents and/or organic solvents can also have been added tothese solutions.

Typical organic solvents which can be added to the developer fluids are,for example, cyclohexanone, 2-ethoxyethanol, toluene, acetone,isopropanol, ethanol and mixtures of two or more of these solvents.

Apart from the greatly reduced delay time effects, the resistcompositions according to the invention are distinguished by goodapplication properties and high optical transparency, high thermalstability and very good resolution power (submicron region).

The protective layers and relief structures produced by using thephotoresist compositions according to the invention represent a furthersubject of the invention.

EXAMPLES 1. Preparation of the Polymers

I.1. Terpolymer of 4-(2-tetrahydropyranyloxy)styrene,N-hydroxymethylmaleimide and N-acetoxymethylmaleimide

In a 100 ml round-bottomed flask, 4.1 g (20 mmol) of4-(2-tetrahydropyranyloxy)styrene, 1.3 g (10 mmol) ofN-hydroxymethylmaleimide, 1.7 g (10 mmol) of N-acetoxymethylmaleimideand 0.3 g of dibenzoyl peroxide are dissolved in 30 ml oftetrahydrofuran (THF). The solution is stirred for 4 hours at 60° C.After cooling to room temperature, the polymer is precipitated in 11 ofmethanol, filtered off and dried. This gives 6.2 g (87%) of a whitepowder which is characterized as follows:

¹ H-NMR (CDCl₃, 300 MHz): δ=6.3-7.4 ppm (m) δ=5.1-5.6 ppm (s, broad)δ=4.7-5.0 ppm (s, broad) δ=3.8-4.0 ppm (s, broad) δ=3.5-3.8 ppm (s,broad) δ=1.2-2.3 ppm (m)

By means of gel permeation chromatography (GPC, polystyrenecalibration), a molecular weight of M_(n) =13 950 (number average) andM_(w) =47 950 (weight average) is measured, from which apolymolecularity index PD=M_(w) /M_(n) of 3.4 results. Thethermogravimetric analysis (TGA, heating rate 10° C./min) shows a weightloss of 32% in the temperature range from 140° to 240° C.

I.2.-I.10. Terpolymers of 4-(2-tetrahydropyranyloxy)styrene,N-hydroxymethylmaleimide and N-acetoxymethylmaleimide

Analogously to Example I.1., terpolymers are prepared with differentmonomer ratios. The quantities of the starting compounds employed andthe yields and measured molecular weights are shown in Table 1 whichfollows.

                                      TABLE 1                                     __________________________________________________________________________    Terpolymen of 4-(2-tetrahydropyanyloxy)styrene, N-hydroxymethylmaleimide      and N-acetoxymethylmaleimide                                                  Example I.2.  I.3.  I.4.  I.5.  I.6.  I.7.  I.8.  I.9   I.10.                 __________________________________________________________________________    4-(2-Tetra-                                                                           20.4 g                                                                              4.8 g 15.0 g                                                                              5.44 g                                                                              67.7 g                                                                              8.2 g 55.7 g                                                                              56.2 g                                                                              10.88 g               hydro-  (100 mmol)                                                                          (20 mmol)                                                                           (73 mmol)                                                                           (27 mmol)                                                                           (332 mmol)                                                                          (40 mmol)                                                                           (273 mmol)                                                                          (276 mmol)                                                                          (53 mmol)             pyranyloxy)                                                                   styrene                                                                       N-Hydroxy-                                                                            88.9 g                                                                              1.78 g                                                                              4.7 g 2.03 g                                                                              16.9 g                                                                              2.03 g                                                                              12.1 g                                                                              7.38 g                                                                              2.71 g                methyl- (70 mmol)                                                                           (14 mmol)                                                                           (37 mmol)                                                                           (16 mmol)                                                                           (132 mmol)                                                                          (16 mmol)                                                                           (95 mmol)                                                                           (58 mmol)                                                                           (21 mmol)             maleimide                                                                     N-Acetoxy-                                                                            5.1 g 1.02 g                                                                              6.2 g 1.81 g                                                                              30.0 g                                                                              4.05 g                                                                              30.0 g                                                                              35.0 g                                                                              4.82 g                methyl- (30 mmol)                                                                           (6 mmol)                                                                            (37 mmol)                                                                           (11 mmol)                                                                           (177 mmol)                                                                          (24 mmol)                                                                           (177 mmol)                                                                          (207 mmol)                                                                          (28.5 mmol)           maleimide                                                                     Dibenzoyl                                                                             1.5 g 0.3 g 1.0 g 0.4 g 4.97 g                                                                              0.6 g 3.9 g 4.0 g 0.8 g                 peroxide                                                                      THF     150 ml                                                                              30 ml 100 ml                                                                              40 ml 500 ml                                                                              60 ml 420 ml                                                                              400 ml                                                                              80 ml                 Yield   79%   87%   84%   81%   87%   85%   73%   68%   85%                   M.sub.n 5300  14,750                                                                              17,000                                                                              18,100                                                                              7420  10,400                                                                              7250  6300  16,050                M.sub.w 34,500                                                                              59,200                                                                              56,650                                                                              63,500                                                                              49,700                                                                              54,300                                                                              37,760                                                                              29,500                                                                              70,520                PD      6.5   4.0   3.3   3.5   6.7   5.2   5.2   4.7   4.4                   __________________________________________________________________________

I.11. Terpolymer of 4-(tert-butylcarbonyloxy)styrene,N-hydroxymethylmaleimide and N-acetoxymethylmaleimide

In an 150 ml round-bottomed flask, 11.0 g (54 mmol) of4-(tert-butylcarbonyloxy)styrene, 1.6 g (12.5 mmol) ofN-hydroxymethylmaleimide, 6.3 g (37.5 mmol) of N-acetoxymethylmaleimideand 0.76 g of dibenzoyl peroxide are dissolved in 80 ml of THF. Thesolution is stirred for 4 hours at 60° C. After cooling to roomtemperture, the polymer is precipitated in 11 of methanol, filtered offand then dissolved in 100 ml of THF. This solution is then slowly addedto 11 of a solvent mixture of n-hexane and toluene. The precipitateformed is filtered off and dried, giving 15.2 g (80%) of a white powder.

¹ H-NMR (CDCl₃, 300 MHz): δ=6.2-7.5 ppm (m) δ=5.3 ppm (s, broad) δ=4.8ppm (s, broad) δ=2.4-3.5 ppm (m) δ=2.0 ppm (s) δ=1.5 ppm (s)

GPC polystyrene calibration): M_(n) =11,950 M_(w) =38,650 PD=3.2

TGA (10° C./min): 27% weight loss in the range from 130°-180° C.

I.12. Terpolymer of 4-tert-butoxystyrene, N-hydroxymethylmaleimide andN-acetoxymethylmaleimide

Analogously to Example I11., 13.9 g (83%) of a white powder are obtainedfrom 8.8 g (50 mmol) of 4-tert-butoxystyrene, 1.6 g (12.5 mmol) ofN-hydroxymethylmaleimide, 6.3 g (37.5 mmol) of N-acetoxymethylmaleimideand 0.67 g of dibenzoyl peroxide, dissolved in 80 ml of THF.

¹ H-NMR (CDCl₃, 300 MHz): δ=6.2-7.3 ppm (m) δ=5.3 ppm (s, broad) δ=4.8ppm (s, broad) δ=2.4-3.6 ppm (m) δ=2.0 ppm (s) δ=1.3 ppm (s)

GPC (polystyrene calibration): M_(n) =18,980 M_(w) =65,150 PD=3.4

TGA (10° C./min): 20% weight loss in the range from 280°-340° C.

I.13. Terpolymer of 4-(3-methylbut-2-enyloxy)styrene,N-hydroxymethylmaleimide and N-acetoxymethylmaleimide

a) Synthesis of 4-(3-methylbut-2-enyloxy)styrene:

In a 500 ml three-necked flask with internal thermometer, nitrogenblanketing and a magnetic stirrer, 22 g (0.4 mol) of KOH powder in 200ml of dimethyl sulfoxide are introduced. 12.0 g (0.1 mol) ofp-hydroxystyrene are then added in portions at 20° C.; 30.0 g (0.2 mol)of 3,3'-dimethylallyl bromide are then added dropwise at 20° C. Afterstirring for 30 minutes at 20° C., 100 g of ice are added slowly. Themixture is then extracted twice with 200 ml of ether. The combinedorganic extracts are washed first with 200 ml of 1N sodium hydroxidesolution and then with 200 ml of water and dried over MgSO₄. Afterremoval of the solvent, the remaining residue is distilled in vacuo(0.07 mbar, 80° C.). This gives 15.5 g (82 mmol, 82%) of a colourlessoil.

¹ H-NMR (CDCl₃, 300 MHz): δ=7.31 ppm (d, 2H) δ=6.85 ppm (d, 2H) δ=6.63ppm (dd, 1H) δ=5.58 ppm (dd, 1H) δ=5.47 ppm (t, 1H) δ=5.09 ppm (dd, 1H)δ=4.47 ppm (d, 2H) δ=1.86 ppm (s, 3H) δ=1.77 ppm (s, 3H)

b) Synthesis of the terpolymer:

Analogously to Example I11., 14.73 g (85%) of a white powder areobtained from 9.4 g (50 mmol) of 4-(3-methylbut-2-enyloxy)styrene, 1.6 g(12.5 mmol) of N-hydroxymethylmaleimide, 6.3 g (37.5 mmol) ofN-acetoxymethylmaleimide and 0.69 g of dibenzoyl peroxide, dissolved in75 ml of THF.

¹ H-NMR (CDCl₃, 300 MHz): δ=6.3-7.4 ppm (m) δ=5.1-5.4 ppm (m) δ=4.4 ppm(s) δ=2.4-3.5 ppm (m) δ=2.0 ppm (s) δ=1.8 ppm (s)

GPC (polystyrene calibration): M_(n) =23,580 M_(w) =235,500 PD=9.9

TGA (10° C./min): 14% weight loss in the range of 260°-320° C.

I.14. Terpolymer of 4-(2-tetrahydropyrranyloxy)styrene,N-hydroxymethylmaleimide and N-(2-acetoxyethyl)maleimide

Analogously to Example I.1., 5.4 g (75%) of a white powder are obtainedfrom 4.1 g (20 mmol) of 4-(2-(tetrahydropyranyloxy)styrene, 1.3 g (10mmol) of N-hydroxymethylmaleimide, 1.8 g (10 mmol) ofN-(2-acetoxyethyl)maleimide and 0.3 g of dibenzoyl peroxide, dissolvedin 30 ml of THF.

¹ H-NMR (CDCl₃, 300 MHz): δ=6.4-7.3 ppm (m) δ=5.35 ppm (s) δ=4.8 ppm (s)δ=3.9 ppm (m) δ=3.6 ppm (m) δ=1.3-3.0 ppm (m)

GPC (polystyrene calibration): M_(n) =8150 M_(w) =59,100 PD=7.2

TGA (10° C./min): 29% weight loss in the range of 180°-230° C. I.15.Terpolymer of 4-(2-tetrahydropyranyloxy)styrene,N-hydroxymethylmaleimide and N-(2-methoxyethyl)maleimide

Analogously to Example I.1., 5.2 g (75%) of a white powder are obtainedfrom 4.1 g (20 mmol) of 4-(2-tetrahydropyranyloxy)styrene, 1.3 g (10mmol) of N-hydroxymethylmaleimide, 1.55 g (10 mmol) ofN-(2-methoxyethyl)maleimide and 0.3 g of dibenzoyl peroxide, dissolvedin 30 ml of THF.

¹ H-NMR (CDCl₃, 300 MHz): δ=6.4-7.3 ppm (m) δ=5.4 ppm (s) δ=4.8 ppm (s)δ=3.9 ppm (m) δ=3.5 ppm (m) δ=3.2 ppm (m) δ=1.3-2.9 ppm (m)

GPC (polystyrene calibration): M_(n) =6660 M_(w) =54,800 PD=8.2

TGA (10° C./min): 30% weight loss in the range of 150°-240° C.

I.16. Terpolymer of 4-(2-tetrahydropyranyloxy)benzyl methacrylate,N-hydroxymethylmaleimide and N-(acetoxymethyl)maleimide

Analogously to Example I.1., 9.3 g (28%) of a white powder are obtainedfrom 21.8 g (79 mmol) of 4-(2-tetrahydropyranyloxy)benzyl methacrylate,6.3 g (49 mmol) of N-hydroxymethylmaleimide, 5.0 g (30 mmol) ofN-(acetoxymethyl)maleimide and 1.0 g of dibenzoyl peroxide, dissolved in130 ml of THF.

¹ H-NMR (CDCl₃, 300 MHz): δ=6.7-7.4 ppm (m) δ=5.4 ppm (s) δ=4.9 ppm (s)δ=3.8 ppm (m) δ=3.6 ppm (m) δ=0.8-3.0 ppm (m)

GPC (polystyrene calibration): M_(n) =4270 M_(w) =13,030 PD=3.0

TGA (10° C./min): 27% weight loss in the range of 150°-300° C.

I.17. Terpolymer of 4-(2-tetrahydropyranyloxy)styrene,N-Hydroxymethylmaleimide and N-(acetoxymethyl)maleimide

Analogously to Example I.1., 7.5 g (80%) of a white powder are obtainedfrom 5.1 g (25 mmol) of 4-(2-tetrahydropyranyloxy)styrene, 0.48 g (4mmol) of N-hydroxymethylmaleimide, 3.59 g (21 mmol) ofN-(acetoxymethyl)maleimide, 0.18 g of dodecanethiol and 0.18 g ofbis-azoisobutyronitrile, dissolved in 64 ml of diglyme.

GPC (polystyrene calibration): M_(n) =9700 M_(w) =20,700 PD=2.1

II. Application Examples

II.1. Positive photoresist

2 g of the polymer from Example I14 and 0.1 g of triphenylsulfoniumtrifluoromethanesulfonate are dissolved in 7 g of cyclopentanone. Thesolution is filtered and spin-coated at 3000 rpm onto a quartz wafer (3inches). The coated quartz wafer is then dried for 2 minutes at 120° C.The layer thickness of the film thus obtained is 1 μm. The coated waferis then exposed imagewise (contact exposure) through a quartz mask withmonochromatic radiation of wavelength 254 nm(10 nm half-width) at adosage of 30 mJ/cm². After exposure, the wafer is subjected on ahotplate for 2 minutes to a temperature of 120° C. and then developed ina 2.38% aqueous tetramethylammonium hydroxide solution, the exposedzones being dissolved out. Structures of 0.5 μm with approximatelyvertical wall profiles are perfectly resolved without formation ofT-topping effects.

II.2. Positive photoresist

1.92 g of the polymer from Example I.17 and 0.08 g of triphenylsulfoniumtrifluoromethanesulfonate are dissolved in 8.0 ml of methoxypropylacetate. The solution is filtered through a filter of 0.5 mm pore sizeand then spin-coated onto a silicon wafer (4 inches), an 850 nm thickresist film resulting after drying at 100° C. for 60 seconds. The coatedwafer is then exposed imagewise with radiation of wavelength 248 nm bymeans of a Canon Excimer Laser Stepper (NA: 0.37) at a dosage of 18mJ/cm². After exposure, the wafer is subjected on a hotplate for 1minute to a temperature of 110° C. and then developed in a 0.262Naqueous tetramethylammonium hydroxide solution, the exposed zones beingdissolved out. In this case, lines/spaces structures of 0.3 μm areresolved with approximately vertical wall profiles, without a residue.

In a second experiment carried out analogously, the heat treatment at110° C. for 1 minute is not carded out until after waiting for one hourafter the exposure. In this case too, lines/spaces structures of 0.3 μmare cleanly resolved, without detectable formation of T-topping effects.

II.3. Positive photoresist

1.92 g of the polymer from Example I.11. and 0.07 g oftriphenylsulfonium trifluoromethanesulfonate are dissolved in 18.7 g ofcyclopentanone. The solution is filtered through a Teflon filter of 0.2μm pore size and then spin-coated onto a silicon wafer (100 mm). Afterheating on the hotplate (60 seconds, 130° C.), a 723 nm thick resistfilm is obtained. The exposure is carded out in optimum focus, using a5:1 projection exposure apparatus (NA 0.37, Canon FPA 4500) at awavelength of 248 nm in exposure steps of 1 mJ/cm². After heating on thehotplate (60 seconds, 120° C.), the exposed wafer is developed for 60seconds in a 0.262N aqueous tetramethylammonium hydroxide solution. Apositive image of the structuring mask is obtained. At an exposuredosage of 16 mJ/cm², sub-half micrometer structures are resolved withsteep edges.

What is claimed is:
 1. A radiation-sensitive composition comprisinga) at least one polymer having a molecular weight (weight average) M_(w) from 10³ to 10⁶, comprising recurring structural units of the formulae (I), (IIa) and (IIb) ##STR13## in which R₁ is hydrogen or methyl, Y is a direct bond or a divalent radical of tho formula ##STR14## in which Z is a C₁ -C₆ alkylene group bound to the phenyl nucleus, OR₂ is an acid-cleavable radical, in which R₂ is C₄ -C₁₀ tert-alkyl, allyl, cyclohex-2-enyl, C₆ -C₁₄ aryl or C₇ -C₁₆ aralkyl which are unsubstituted or mono- or poly-substituted by C₁ -C₆ alkyl groups, C₁ -C₆ alkoxy groups or halogen atoms, trialkysilyl or a group of the formulae (IV)-(VII) ##STR15## in which R₈ is C₁ -C₆ alkyl, or C₆ C₁₄ aryl or C₇ -C₁₆ aralkyl which are unsubstituted or mono- or poly-substituted by C₁ -C₆ alkyl groups, C₁ -C₆ alkoxy groups or halogen atoms. R₃ and R₄ independently of one another are hydrogen, C₁ -C₆ alkyl groups, C₁ -C₆ alkoxy groups or halogen atoms, R₅ and R₆ independently of one another are hydrogen or methyl, X is C₁ -C₆ alkylene and R₇ is C₁ -C₆ alkyl, or C₆ -C₁₄ aryl or C₇ -C₁₆ aralkyl which are unsubstituted or mono- or poly-substituted by C₁ -C₆ alkyl groups, C₁ -C₆ alkoxy groups or halogen atoms, or is --CO--R₈ in which R₈ is as defined in formula (IV), and b) at least one compound which generates an acid under the action of actinic radiation.
 2. A composition according to claim 1, comprising a solvent or solvent mixture as a further component c).
 3. A composition according to claim 1, comprising as component b) at least one compound of the formula (VIII)

    (Ar.sub.1).sub.q (Z.sub.1).sub.r (Z.sub.2).sub.s S.sup.⊖ X.sub.1.sup.⊕                                         (VIII),

in which Ar₁ is phenyl, naphthyl or phenyl-COCH₂ --, which are unsubstituted or substituted by halogen, C₁ -C₄ alkyl, C₁ -C₄ alkoxy,--OH and/or nitro, Z₁ is C₁ -C₆ alkyl or C₃ -C₇ cycloalkyl and Z₂ is tetrahydrothienyl, tetrahydrofuryl or hexahydropyryl, q is 0, 1, 2 or 3, r is 0, 1 or 2 and s is 0 or 1, the sum q+r+s being 3, and X₁.sup.⊖ is a chloride, bromide or iodide anion, BF₄.sup.⊖, PF₆.sup.⊖, AsF₆.sup.⊖, SbF₆.sup.⊖, FSO.sup.⊖ or the anion of an organic sulfonic acid or carboxylic acid.
 4. A composition according to claim 3, in which Ar₁ is phenyl, q is the number 3, r and s are zero and X₁.sup.⊖ is SbF₆.sup.⊖, AsF₆.sup.⊖, PF₆.sup.⊖, CF₃ SO₃.sup.⊖, C₂ F₅ SO₃.sup.⊖, n--C₃ F₇ SO₃.sup.⊖ n--C₄ F₉ SO₃.sup.⊖, n--C₆ F₁₃ SO₃.sup.⊖, n--C₈ F₁₇ SO₃.sup.⊖ or C₆ F₅ SO₃.sup.⊖.
 5. A composition according to claim 3, in which the component b) is triphenylsulfonium trifluoromethanesulfonate.
 6. A composition according to claim 1, comprising 0.1-20% by weight, preferably 1-10% by weight, of component b), relative to the weight of component a).
 7. The protective layers and relief structures produced by using the composition according to claim
 1. 